You have varied the duty cycle, but the frequency remains the same, namely 490 Hz.

I don't see the significance of this 111Hz from what you've said so far.

Edit.In case you don't understand the difference, consider a signal with one millisecond high, and nine milliseconds low. The frequency is 100Hz, and the duty cycle is 10%.A signal with nine milliseconds high and one millisecond low has the same frequency, but a 90% duty cycle.

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.Do not send technical questions via personal messaging - they will be ignored.